Carcinogenesis Advance Access published online on September 10, 2008
Carcinogenesis, doi:10.1093/carcin/bgn214
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Artemisinin selectively decreases functional levels of estrogen receptor-alpha and ablates estrogen induced proliferation in human breast cancer cells
Department of Molecular and Cell Biology and the Cancer Research Laboratory, University of California at Berkeley, Berkeley, CA 94720
Requests for reprints: Gary L. Firestone, Dept. Molecular and Cell Biology, 591 LSA, University of California at Berkeley, Berkeley, CA 94720-3200. Phone: (510) 642-8319, FAX: (510) 643-6791, Email: glfire{at}berkeley.edu
MCF7 cells are an estrogen responsive human breast cancer cell line that expresses both estrogen receptor-alpha (ER
) and estrogen receptor-beta (ERβ). Treatment of MCF7 cells with artemisinin, an anti-malarial phytochemical from the sweet wormwood plant, effectively blocked estrogen stimulated cell cycle progression induced by either 17β-estradiol (E2), an agonist for both estrogen receptors, or by propyl pyrazole triol (PPT), a selective ER agonist. Artemisinin strongly down-regulated ER protein and transcripts without altering expression or activity of ERβ. Transfection of MCF7 cells with ER promoter-linked luciferase reporter plasmids revealed that the artemisinin down-regulation of ER promoter activity accounted for the loss of ER expression. Artemisinin treatment ablated the estrogenic induction of endogenous progesterone receptor transcripts by either E2 or PPT, and inhibited the estrogenic stimulation of a luciferase reporter plasmid driven by consensus estrogen response elements (ERE). Chromatin immunoprecipitation assays revealed that artemisinin significantly down-regulated the level of endogeneous ER bound to the progesterone receptor promoter, whereas the level of bound endogeneous ERβ was not altered. Treatment of MCF7 cells with artemisinin and the pure antiestrogen, fulvestrant resulted in a cooperative reduction of ER protein levels and enhanced G1 cell cycle arrest compared to the effects of either compound alone. Our results show that artemisinin switches proliferative human breast cancer cells from expressing a high ER:ERβ ratio to a condition in which ERβ predominates, which parallels the physiological state linked to anti-proliferative events in normal mammary epithelium.
Key Words: Artemisinin • breast cancer cells • proliferation • Estrogen Receptor-alpha • Estrogen Receptor-beta • Progesterone Receptor
Grant Support: This study was supported by grant 12IB-0166 awarded from the California Breast Cancer Research Program. In the early stages of the work, S.N.S. was a recipient of a pre-doctoral fellowship supported by NIH National Research Service Grant CA09041.
Received April 21, 2008; revised September 2, 2008; accepted September 6, 2008.